The Study on Osteoarthritis Progression Prevention (STOPP) involved 622 patients in Europe and the US, ages 45-80 years, with knee arthritis. On average, the patients reported moderate levels of pain when the study began.

Patients were randomly assigned to 2 years of daily treatment with chondroitin or inactive “placebo.” X-rays of the affected knee were taken to assess the impact of treatment.

Pain relief increased with time in the chondroitin group, lead author Dr. Andre Kahan, at Cochin Hospital in Paris, and colleagues report. Moreover, treatment with chondroitin reduced the likelihood of joint narrowing — indicating a loss of cartilage — by 33 percent.

Over 90 percent of the subjects reported good or very good tolerability with chondroitin, and side effects were no more likely than with placebo.

The authors note that because the chondroitin used in the STOPP trial is a prescription drug, the results cannot be generalized to chondroitin products sold as dietary supplements.